1. Field of the Invention
This invention relates to polycarboyxlic acid compositions. More particularly, the invention is concerned with anhydrides and esters of alkyl or cycloalkyl tetracarboxylic acids which esters are useful as plasticizers in polyvinyl chloride plastic compositions.
2. Description of the Prior Art
Resins such as polyvinyl chloride and its copolymers are widely employed in the field of plastics materials. Such resins are generally hard and somewhat brittle by nature, and it is customary to add plasticizing agents to improve their workability during forming operations. Ordinarily some of the plasticizer is retained in the product formed where it characteristically provides certain desirable properties to the product. Among these characteristics is the ability of the plasticizer to impart low-temperature flexibility. Also the plasticizer must be characterized by low volatility to prevent its loss by evaporation. Furthermore, the plasticizer should be compatible with the resin and resist extraction when contacted with hydrocarbons or water. Vinyl chloride polymers in particular have been plasticized with tetra-alkyl alkenyl tetracarboxylates which are addition products of dialkyl fumarates and dialkyl alkenyl succinates. See, for instance, U.S. Pat. No. 2,806,011.
Esters of polycarboxylic acids have been suggested for use as synthetic lubricants. In general, they are characterized by higher viscosity indices, lower pour points and higher flash points and mineral oils of corresponding viscosity. Dialkyl alkenyl succinates prepared from the alkenyl succinic acid anhydride in particular have been suggested for this purpose. See, for instance, U.S. Pat. No. 2,561,232.